The invention relates generally to the field of image processing, and in particular to detecting hidden messages embedded in digital images or printed images. This field is also referred to as data hiding, data embedding, information hiding, watermarking and also steganography.
U.S. Pat. No. 6,044,156, issued Mar. 28, 2000, entitled xe2x80x9cMethod For Generating An Improved Carrier For Use In An Image Data Embedding Application,xe2x80x9d by Honsinger et al., discloses a technique for embedding messages in digital images data. This method for embedding a hidden message into a digitized image includes the steps of: forming a digitized version of the desired message; generating a random phase carrier; convolving the digitized version of the desired message and the random phase carrier to form a dispersed message; and combining the dispersed message with the digitized image to form an image with an embedded hidden message. Hidden messages may be embedded in photographic images recorded on film and paper using conventional photographic printing techniques, or they may be embedded in images produced on printers such as ink jet and thermal dye transfer printers, by combining the dispersed message with a digital image using digital image processing techniques. The hidden or embedded information can include copyright or proprietor information or other information associated with the digital image.
The hidden messages are recovered from the image by cross correlating the image containing the dispersed message with a decoding carrier to recover the embedded dispersed message and extracting the digital message data from the recovered dispersed message.
Several embedding software can be used for embedding messages in digital images, for example, the techniques disclosed in U.S. Pat. No. 5,636,292, issued Jun. 3, 1997, to Rhoads, entitled xe2x80x9cSteganography Methods Employing Embedded Calibration Data,xe2x80x9d and U.S. Pat. No. 5,859,920, issued Jan. 12, 1999 to Daly et al., and entitled xe2x80x9cMethod for Embedding Digital Information in an Image.xe2x80x9d The extraction of information embedded using different manufacturers requires keys produced by these manufacturers. A problem thus exists if not all the keys are available at an imaging devicexe2x80x94if the embedded information relates to a copyright in the image, the copyright information on some digital images cannot be detected. There is therefore a need to detect the existence of embedded messages in a digital image produced by any manufacturer""s embedding software, regardless of the source of the embedded software.
The above noted need is met according to the present invention by providing a method of detecting an embedded message in a digital image, the embedded message being embedded in periodic blocks in the image, that includes the steps of: selecting a first area in the digital image; selecting a second area in the digital image; performing a correlation between the first and the second image areas; and if the correlation exceeds an predetermined threshold value at at least one pixel location, producing a signal indicating the existence of embedded message in the digital image.
An advantage of the present invention is that existence of messages embedded in digital images can be detected. Proper warning and measures can be taken for protecting the potential copyright of the digital images.
Another advantage of the present invention is that the present invention can detect the existence of embedded messages produced by different manufacturers"" software.